Gas Sensor

Abstract

To improve water resistance of a sensor element in a gas sensor. [Solution] A gas sensor (100) includes a sensor element (110), an inner protective cover (130) having a sensor element chamber (124) therein and an element chamber inlet (125) disposed therein, in which the front end of the sensor element (110) is disposed, and an outer protective cover (140) having an outer inlet (144a). The inner protective cover (130) includes a first member (131) and a second member (135) surrounding the periphery of the first member (131). The element chamber inlet (125) has a first inlet (127) configured as a gap between the first member (131) and the second member (135). The first member (131) includes a first cylindrical portion (134) surrounding the periphery of the sensor element (110), and a bottom portion (134a) disposed below the first cylindrical portion (134) and the sensor element (110) and having an opening (134c). An opening area (Sf) of the opening (134c) is smaller than a cross-sectional area (S0) perpendicular to the axial direction of the space inside the first cylindrical portion (134).

Description

[Technical Field]

[0001] The present invention relates to a gas sensor. [Background technology]

[0002] Conventionally, gas sensors that detect the concentration of specific gases such as NOx and oxygen in a measurement gas such as automobile exhaust gas have been known. For example, Patent Document 1 describes a gas sensor including a sensor element, an inner protective cover in which the tip of the sensor element is disposed, and an outer protective cover disposed outside the inner protective cover. The inner protective cover has a sensor element chamber inside in which the tip of the sensor element is disposed, and is provided with an element chamber inlet that is an entrance to the sensor element chamber and an element chamber outlet that is an exit from the sensor element chamber. The outer protective cover is provided with an outer inlet that is an entrance from the outside of the measurement gas and an outer outlet that is an exit for the measurement gas to the outside. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 7465739 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in such gas sensors, water may get inside the protective cover and adhere to the sensor element, causing cracks in the sensor element. Therefore, there has been a demand for preventing water from adhering to the sensor element, i.e., for improving the water resistance of the sensor element.

[0005] The present invention has been made to solve the above problems, and has as its main object to improve the water resistance of a sensor element in a gas sensor. [Means for solving the problem]

[0006] In order to achieve the above-mentioned main object, the present invention employs the following means.

[0007] [1] The gas sensor of the present invention is a sensor element having a front end and a rear end opposite to the front end, the sensor element having a gas inlet for introducing a measurement gas, the sensor element detecting a specific gas concentration of the measurement gas flowing into the sensor element through the gas inlet; a cylindrical inner protective cover having a sensor element chamber therein in which the front end of the sensor element and the gas inlet are disposed, the sensor element chamber having an element chamber inlet which is an inlet to the sensor element chamber and an element chamber outlet which is an outlet from the sensor element chamber; a cylindrical outer protective cover having an outer inlet through which the measurement gas enters from the outside and an outer outlet through which the measurement gas exits to the outside, the outer protective cover being disposed outside the inner protective cover; Equipped with the outer protective cover and the inner protective cover form an inlet-side gas flow path from the outside to the sensor element chamber, which includes the outer inlet and the element chamber inlet, and an outlet-side gas flow path from the sensor element chamber to the outside, which includes the element chamber outlet and the outer outlet, the inner protective cover includes a cylindrical first member that surrounds the sensor element, and a cylindrical second member that surrounds the first member and has the element chamber outlet, the element chamber inlet has a first inlet configured as a gap between the first member and the second member; an opening of the first inlet on the sensor element chamber side is parallel to the axial direction of the first member and opens downward, which is a direction from the rear end toward the front end of the sensor element; the first member has a first cylindrical portion surrounding the sensor element, and a bottom portion disposed below the first cylindrical portion and the sensor element and having an opening, An opening area Sf of the opening of the bottom portion is smaller than a cross-sectional area S0 perpendicular to the axial direction of the space inside the first cylindrical portion. It is something.

[0008] In this gas sensor, the inner protective cover has a sensor element chamber therein and an element chamber inlet that is an entrance to the sensor element chamber. The inner protective cover has a cylindrical first member that surrounds the sensor element and a cylindrical second member that surrounds the first member. The element chamber inlet has the first inlet configured as a gap between the first and second members. The first member has a first cylindrical portion that surrounds the sensor element and a bottom portion that is disposed below the first cylindrical portion and the sensor element and has an opening. The opening area Sf of the bottom opening is smaller than the cross-sectional area S0 of the space inside the first cylindrical portion perpendicular to the axial direction. The presence of such a bottom in the first member prevents water from adhering to the sensor element when it enters the sensor element chamber through the first inlet. This improves the water resistance of the sensor element in the gas sensor. Furthermore, since the bottom portion has an opening, the measurement gas that passes through the first inlet can reach the sensor element through the opening. Here, "opening downward" includes a case where the opening is parallel to the downward direction, and a case where the opening is inclined from the downward direction so as to approach the sensor element as it goes downward.

[0009] [2] In the above-mentioned gas sensor (the gas sensor described in [1]), the bottom portion may have a shape in which the inner diameter tends to decrease in the downward direction, and the opening may be provided at the downward end portion.

[0010] [3] In the above-described gas sensor (the gas sensor according to [2] above), the bottom portion may have a tapered portion whose inner diameter decreases in the downward direction.

[0011] [4] In the gas sensor (the gas sensor according to any one of [1] to [3]), the opening area Sf is 61.93 mm 2 In this way, the effect of improving the water resistance of the sensor element can be more reliably obtained.

[0012] [5] In the gas sensor described above (the gas sensor described in any one of [1] to [4]), the opening area Sf is 28.27 mm 2 This further improves the water resistance of the sensor element.

[0013] [6] In the gas sensor described above (the gas sensor described in any one of [1] to [5]), the opening area Sf is 8.45 mm 2 If the opening area Sf is too small, the time it takes for the gas to pass through the opening and reach the sensor element increases, which may result in a decrease in the response of the sensor element to detect the concentration of a specific gas. 2 By exceeding the limit, it is possible to suppress a decrease in the responsiveness of the detection of the concentration of the specific gas.

[0014] [7] In the gas sensor described above (the gas sensor described in any one of [1] to [6]), the opening area Sf is 12.57 mm 2 This makes it possible to more reliably prevent a decrease in the response of the specific gas concentration detection.

[0015] [8] In the above-described gas sensor (the gas sensor according to any one of [1] to [7]), the element chamber inlet may have a second inlet disposed in the first member. In this case, since the element chamber inlet has not only the first inlet but also the second inlet, the measurement gas can more easily flow into the sensor element chamber. This makes it possible to suppress a decrease in the responsiveness of the sensor element in detecting the concentration of a specific gas.

[0016] [9] In the gas sensor described above (the gas sensor described in [8] above), the second inlet may be located above the first inlet, in a direction opposite to the downward direction.

[0017]

[10] In the gas sensor described in [8] or [9] above, the opening area Ss of the second inlet is 10.60 mm 2This makes it difficult for water to enter the sensor element chamber through the second inlet, so that the water resistance of the sensor element is unlikely to decrease even if the second inlet is present.

[0018]

[11] In the gas sensor described above (the gas sensor described in any one of [8] to

[10] ), the opening area Ss of the second inlet is 7.36 mm 2 This can further prevent the deterioration of water resistance of the sensor element due to the presence of the second inlet.

[0019]

[12] In the gas sensor described above (the gas sensor described in any one of [8] to

[11] ), the opening area Ss of the second inlet is 1.18 mm 2 In this way, the presence of the second inlet can more reliably suppress a decrease in responsiveness in detecting the concentration of a specific gas.

[0020]

[13] In the gas sensor (the gas sensor according to any one of [8] to

[12] ), the opening area Ss of the second inlet is 2.65 mm 2 In this case, the presence of the second inlet can further enhance the effect of suppressing a decrease in responsiveness in detecting the concentration of the specific gas.

[0021]

[14] In the above-described gas sensor (the gas sensor according to any one of [1] to

[13] above), the inlet-side gas flow path may have a first flow path that is a space between the outer protective cover and the inner protective cover and that faces upward from the outer inlet in a direction opposite to the downward direction, and the inner protective cover and / or the outer protective cover may have a water passage suppression portion that is disposed above the outer inlet in the first flow path and that has a shape that narrows a part of the first flow path. In this way, the water resistance of the sensor element can be improved not only by the bottom of the first member but also by the water passage suppression portion. [Brief explanation of the drawings]

[0022] [Figure 1]FIG. 2 is a schematic explanatory diagram of a state in which the gas sensor 100 is attached to the pipe 10. [Figure 2] Cross section AA of Figure 1. [Figure 3] Cross section B-B of Figure 2. [Figure 4] Cross section CC of Figure 3. [Figure 5] DD cross section of Figure 3. [Figure 6] View from E in Figure 3. [Figure 7] Enlarged view of a portion of Figure 3. [Figure 8] 10 is an explanatory diagram showing a state in which water W has accumulated inside the inner protective cover 130. FIG. [Figure 9] FIG. 1 is a vertical cross-sectional view of a gas sensor 900 of a comparative example. [Figure 10] FIG. 10 is a vertical cross-sectional view of a gas sensor 200 according to a modified example. [Figure 11] FIG. 10 is a vertical cross-sectional view of a gas sensor 300 according to a modified example. [Figure 12] FIG. 10 is a partial cross-sectional view of an outer inlet 144a having a square hole 144d. DETAILED DESCRIPTION OF THE INVENTION

[0023] Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic explanatory diagram of a state in which a gas sensor 100 is attached to a pipe 10. FIG. 2 is a cross-sectional view taken along line AA in FIG. 1. FIG. 3 is a cross-sectional view taken along line BB in FIG. 2. FIG. 4 is a cross-sectional view taken along line CC in FIG. 3. FIG. 5 is a cross-sectional view taken along line DD in FIG. 3. FIG. 6 is a view seen from line E in FIG. 3. FIG. 7 is a partially enlarged view of FIG. 3. Note that the direction parallel to the axial direction of the protective cover 120 (particularly the first member 131 of the inner protective cover 130) and from the front end to the rear end of the sensor element 110 (the upward direction in FIGS. 3 and 7) is defined as the upward direction, and the direction parallel to the axial direction of the protective cover 120 (particularly the first member 131 of the inner protective cover 130) and from the rear end to the front end of the sensor element 110 (the downward direction in FIGS. 3 and 7) is defined as the downward direction.

[0024] As shown in Fig. 1, the gas sensor 100 is attached to a pipe 10, which is an exhaust path from a vehicle engine, and is configured to detect the concentration of a specific gas contained in exhaust gas, which is a measurement gas emitted from the engine. Examples of the specific gas include NOx, ammonia, and O2. As shown in Fig. 2, the gas sensor 100 is fixed in the pipe 10 with its central axis perpendicular to the flow of the measurement gas in the pipe 10. Alternatively, the gas sensor 100 may be fixed in the pipe 10 with its central axis perpendicular to the flow of the measurement gas in the pipe 10 and tilted at a predetermined angle (e.g., 45° or 60°) relative to the vertical direction.

[0025] As shown in FIG. 3 , the gas sensor 100 includes a sensor element 110 and a protective cover 120 that protects the sensor element 110. The gas sensor 100 also includes an element encapsulation body 101 that encapsulates and fixes the sensor element 110, and bolts 103 attached to the element encapsulation body 101. The element encapsulation body 101 includes a cylindrical metal housing 102, a ceramic supporter 104 that is sealed in a through-hole inside the housing 102, and a powder compact 105 that is molded from ceramic powder such as talc and that is sealed in the through-hole inside the housing 102. The sensor element 110 is located on the central axis of the element encapsulation body 101 and penetrates the element encapsulation body 101 in the vertical direction. The powder compact 105 is compressed between the housing 102 and the sensor element 110. As a result, the powder compact 105 seals the through-hole in the housing 102 and fixes the sensor element 110. Bolt 103 is a cylindrical metal member with a male thread on its outer periphery. Housing 102 of element sealing body 101 is welded to pipe 10 and inserted into fixing member 12, which is welded to pipe 10 and has a female thread on its inner periphery. Bolt 103 is further screwed into fixing member 12, thereby fixing housing 102 in fixing member 12. In this way, gas sensor 100 is fixed in pipe 10. The direction of flow of the measurement gas in pipe 10 is from left to right in FIG. 3.

[0026] The sensor element 110 includes an element body 20 and a porous protective layer 22 covering at least a portion of the surface of the element body 20. The element body 20 is an elongated, long, plate-like element and has a structure in which multiple oxygen-ion conductive solid electrolyte layers, such as zirconia (ZrO), are stacked. The element body 20 has a gas inlet 21 through which a measurement gas is introduced into the element body 20 and is configured to be able to detect the concentration of a specific gas in the measurement gas that flows into the element body 20 through the gas inlet 21. In this embodiment, the gas inlet 21 is open at the front end face of the element body 20 (the lower end face of the element body 20 in FIG. 3). The element body 20 includes a heater therein that heats and maintains the temperature of the element body 20 and serves to regulate the temperature. The structure of the element body 20 and the principle of detecting the concentration of a specific gas are known, and are described, for example, in Japanese Patent Application Laid-Open No. 2008-164411. The front end (the lower end in FIG. 3) and the gas inlet 21 of the sensor element 110 are disposed in the sensor element chamber 124 .

[0027] In this embodiment, the porous protective layer 22 is formed on five of the six surfaces of the element body 20, covering most of the surface of the element body 20 exposed in the sensor element chamber 124. Specifically, the porous protective layer 22 covers the entire front end surface (lower surface) of the element body 20, on which the gas inlet 21 is formed. Furthermore, of the four surfaces connected to the front end surface of the element body 20 (the top, bottom, left, and right surfaces of the element body 20 in FIG. 4 ), the porous protective layer 22 covers the side closest to the front end surface of the element body 20. The porous protective layer 22 serves to, for example, prevent moisture and the like in the gas under measurement from adhering to the element body 20, causing cracks. The porous protective layer 22 also serves to prevent oil components and the like contained in the gas under measurement from adhering to electrodes (not shown) on the surface of the element body 20. The porous protective layer 22 is made of a porous material such as porous alumina, porous zirconia, porous spinel, porous cordierite, porous titania, or porous magnesia. The porous protective layer 22 can be formed by, for example, plasma spraying, screen printing, dipping, etc. The porous protective layer 22 also covers the gas inlet 21, but since the porous protective layer 22 is a porous body, the gas to be measured can flow through the inside of the porous protective layer 22 and reach the gas inlet 21.

[0028] The protective cover 120 is disposed to surround the sensor element 110. The protective cover 120 includes a cylindrical inner protective cover 130 with a bottom that covers the front end of the sensor element 110, and a cylindrical outer protective cover 140 with a bottom that covers the inner protective cover 130. A sensor element chamber 124 is formed as a space surrounded by the inner protective cover 130. The outer protective cover 140 and the inner protective cover 130 form an inlet gas flow path 152, which is a flow path for the measurement gas from the outside to the sensor element chamber 124, and an outlet gas flow path 156, which is a flow path for the measurement gas from the sensor element chamber 124 to the outside. A first gas chamber 122 and a second gas chamber 126 are also formed as spaces surrounded by the inner protective cover 130 and the outer protective cover 140. The first gas chamber 122 is part of the inlet gas flow path 152, and the second gas chamber 126 is part of the outlet gas flow path 156. The gas sensor 100, the sensor element 110, the inner protective cover 130, and the outer protective cover 140 are coaxial with each other. The protective cover 120 is made of metal (for example, stainless steel such as SUS310S).

[0029] The inner protective cover 130 includes a first member 131 and a second member 135. The first member 131 includes a cylindrical large-diameter portion 132, a cylindrical first cylindrical portion 134 having a diameter smaller than that of the large-diameter portion 132, a step portion 133 connecting the large-diameter portion 132 and the first cylindrical portion 134, and a bottom portion 134a disposed below the first cylindrical portion 134. The first cylindrical portion 134 surrounds the sensor element 110. The bottom portion 134a is disposed below the sensor element 110. The central axis of the bottom portion 134a is coaxial with that of the first cylindrical portion 134. The upper end of the bottom portion 134a is connected to the lower end of the first cylindrical portion 134. The bottom portion 134a includes a tapered portion 134b and an opening 134c. The tapered portion 134b has a shape in which the inner diameter decreases downward. The opening 134c is a circular hole disposed at the lower end of the bottom portion 134a. The central axis of the opening 134c is coaxial with that of the first cylindrical portion 134. The diameter of the opening 134c is smaller than the inner diameter of the first cylindrical portion 134 and the inner diameter of the upper end of the bottom portion 134a. Therefore, the opening area Sf of the opening 134c is smaller than the cross-sectional area S0 of the space inside the first cylindrical portion 134, which is perpendicular to the up-down direction (the axial direction of the first member 131). The cross-sectional area S0 is the area of ​​a circle whose outer shape is the inner circumferential surface of the first cylindrical portion 134 shown in FIG. 4, and the opening area Sf is the area of ​​the circle of the opening 134c shown in FIG. 5.

[0030] The second member 135 has a second cylindrical portion 136 having a larger diameter than the first cylindrical portion 134, a third cylindrical portion 137 having a smaller diameter than the second cylindrical portion 136, and a tip portion 138 having a smaller diameter than the third cylindrical portion 137. The second member 135 also has a step portion 136c connecting the lower end of the second cylindrical portion 136 to the upper end of the third cylindrical portion 137, and a step portion 137a connecting the lower end of the third cylindrical portion 137 to the upper end of the tip portion 138. The tip portion 138 has a side portion 138d and a bottom portion 138e. An element chamber outlet 138a is formed in the tip portion 138 and communicates with the sensor element chamber 124 and the second gas chamber 126, and is an outlet for the measurement gas from the sensor element chamber 124. The element chamber outlet 138a has a plurality of (four in this embodiment) circular horizontal holes 138b formed at equal intervals around the circumferential direction of the side portion 138d. The element chamber outlet 138a is not disposed at the bottom portion 138e of the tip portion 138. The diameter of the horizontal holes 138b is, for example, 0.5 mm to 2.6 mm. In this embodiment, the diameters of the multiple horizontal holes 138b are all the same. The element chamber outlet 138a is disposed below the gas inlet 21. In other words, the element chamber outlet 138a is located farther (downward) than the gas inlet 21 when viewed from the rear end of the sensor element 110 (the upper end, not shown, of the sensor element 110 in FIG. 3).

[0031] The large diameter portion 132, the first cylindrical portion 134, the second cylindrical portion 136, the third cylindrical portion 137, and the tip portion 138 share the same central axis. The inner circumferential surface of the large diameter portion 132 abuts against the housing 102, thereby fixing the first member 131 to the housing 102. The outer circumferential surface of the third cylindrical portion 137 of the second member 135 abuts against the inner circumferential surface of the outer protective cover 140, and the second member 135 is fixed by welding or the like. Note that the outer diameter of the third cylindrical portion 137 may be formed slightly larger than the inner diameter of the tip portion 146 of the outer protective cover 140, and the third cylindrical portion 137 may be press-fitted into the tip portion 146 to fix the second member 135.

[0032] The inner circumferential surface of the second cylindrical portion 136 is formed with a plurality of protrusions 136a that protrude toward and contact the outer circumferential surface of the first cylindrical portion 134. As shown in FIG. 4 , four protrusions 136a are provided, evenly spaced along the circumferential direction of the inner circumferential surface of the second cylindrical portion 136. The protrusions 136a are formed in a generally hemispherical shape. The provision of such protrusions 136a facilitates fixing the positional relationship between the first cylindrical portion 134 and the second cylindrical portion 136. Preferably, the protrusions 136a press the outer circumferential surface of the first cylindrical portion 134 radially inward. This more reliably fixes the positional relationship between the first cylindrical portion 134 and the second cylindrical portion 136. The number of protrusions 136a is not limited to four, and may be two, three, five, or more. It is preferable to provide three or more protruding portions 136a, as this facilitates stable fixation between the first cylindrical portion 134 and the second cylindrical portion 136.

[0033] The inner protective cover 130 has an element chamber inlet 125 that communicates with the first gas chamber 122 and the sensor element chamber 124 and is an inlet for the measurement gas into the sensor element chamber 124. The element chamber inlet 125 is a part of the inlet-side gas flow path 152. The element chamber inlet 125 has a first inlet 127 and a second inlet 128 (see FIGS. 3, 4, and 7). The first inlet 127 is a space between the first member 131 and the second member 135. More specifically, the first inlet 127 is formed as a cylindrical gap (gas flow path) between the outer circumferential surface of the first cylindrical portion 134 and the inner circumferential surface of the second cylindrical portion 136. The first inlet 127 is a space from the upper end of the second cylindrical portion 136 of the second member 135 to the lower end of the first cylindrical portion 134 of the first member 131. The first inlet 127 has an upper opening 127a which is an opening on the side of the first gas chamber 122, which is the space where the outer inlet 144a is arranged, and a lower opening 127b which is an opening on the side of the sensor element chamber 124, which is the space where the gas inlet 21 is arranged. The upper opening 127a is a ring-shaped gap between the upper end of the inner circumferential surface of the second cylindrical portion 136 and the outer circumferential surface of the first cylindrical portion 134. The lower opening 127b is a ring-shaped gap between the inner circumferential surface of the second cylindrical portion 136 and the lower end of the outer circumferential surface of the first cylindrical portion 134. The upper opening 127a is formed closer to the rear end (upper side) of the sensor element 110 than the lower opening 127b. Therefore, in the path of the measurement gas from the outer inlet 144a to the gas inlet 21, i.e., in the inlet-side gas flow path 152, the first inlet 127 forms a flow path from the rear end (upper side) to the front end (lower side) of the sensor element 110. The first inlet 127 also forms a flow path parallel to the rear end and front end of the sensor element 110 (a flow path parallel to the up-down direction). The lower opening 127b opens into the sensor element chamber 124.

[0034] The lower opening 127b opens in a direction (downward) from the rear end to the front end of the sensor element 110 and is parallel to the rear-to-front end direction (up-down direction) of the sensor element 110. That is, the lower opening 127b opens parallel to the downward direction. Therefore, the sensor element 110 is disposed at a position other than the region obtained by virtually extending the first inlet 127 from the lower opening 127b (the region directly below the lower opening 127b in FIGS. 3 and 7).

[0035] The second inlet 128 is disposed in the first member 131. More specifically, the second inlet 128 is a plurality of (six in this example) horizontal holes formed at equal intervals along the outer periphery of the first cylindrical portion 134. The second inlet 128 is located above the first inlet 127. More specifically, the second inlet 128 is located above an upper opening 127a of the first inlet 127. The second inlet 128 is located above the front end (the lower end in FIG. 3 ) of the sensor element 110 and the gas inlet 21.

[0036] As shown in FIG. 3 , the outer protective cover 140 has a cylindrical body portion 143 and a bottomed, cylindrical tip portion 146 having a smaller inner diameter than the body portion 143. The body portion 143 also has a side portion 143a having a side surface along the central axis direction (vertical direction) of the outer protective cover 140, and a step portion 143b which is the bottom of the body portion 143 and connects the side portion 143a to the tip portion 146. The central axes of the body portion 143 and the tip portion 146 are both the same as the central axis of the inner protective cover 130. The inner circumferential surface of the upper end portion of the body portion 143 abuts against the housing 102 and the large diameter portion 132, thereby fixing the outer protective cover 140 to the housing 102. The body portion 143 is positioned so as to cover the outer peripheries of the large diameter portion 132, the first cylindrical portion 134, and the second cylindrical portion 136. The tip portion 146 is positioned to cover the tip portion 138, and its inner peripheral surface abuts against the outer peripheral surface of the third cylindrical portion 137. The tip portion 146 has a side portion 146a that has a side surface along the central axis direction (vertical direction) of the outer protective cover 140 and has an outer diameter smaller than the inner diameter of the side portion 143a, and a bottom portion 146b that is the bottom of the outer protective cover 140. The bottom portion 146b has a tapered portion 146c that narrows in diameter from the side portion 146a toward the lower end of the bottom portion 146b. The tip portion 146 is positioned below the body portion 143. The outer protective cover 140 has one or more (multiple, specifically 12 in this embodiment) outer inlets 144a formed in the body portion 143 as inlets for the measurement gas from the outside, and one or more outer outlets 147a formed in the tip portion 146 as outlets for the measurement gas to the outside.

[0037] The outer inlet 144a is a hole that communicates with the outside (outside) of the outer protective cover 140 and the first gas chamber 122. The outer inlet 144a has a plurality of (six in this embodiment) horizontal holes 144b formed at equal intervals in the side portion 143a and a plurality of (six in this embodiment) vertical holes 144c formed at equal intervals in the step portion 143b (see FIGS. 3, 5, and 6). The horizontal holes 144b open in a direction that intersects the vertical direction, and in this embodiment, open in a direction that intersects perpendicularly with the vertical direction. The vertical holes 144c open along the vertical direction, and in this embodiment, open parallel to the vertical direction. The outer inlets 144a (horizontal holes 144b and vertical holes 144c) are circular holes. The diameter of the twelve outer inlets 144a is, for example, 0.5 mm to 2 mm. The diameter of the outer inlets 144a may be 1.5 mm or less. In this embodiment, the diameters of the horizontal holes 144b are all the same, and the diameters of the vertical holes 144c are all the same. The diameter of the horizontal holes 144b is larger than the diameter of the vertical holes 144c. As shown in FIG. 5, the outer inlet 144a is formed so that the horizontal holes 144b and the vertical holes 144c are alternately positioned at equal intervals along the circumferential direction of the outer protective cover 140. That is, the angle formed by the line connecting the center of the horizontal hole 144b to the central axis of the outer protective cover 140 and the line connecting the center of the vertical hole 144c adjacent to that horizontal hole 144b to the central axis of the outer protective cover 140 in FIG. 5 is 30° (360° / 12 holes).

[0038] The outer outlet 147a is a hole that communicates with the outside (outside) of the outer protective cover 140 and the second gas chamber 126. The outer outlet 147a has one or more vertical holes 147c (one in this embodiment) formed in the center of the bottom 146b of the tip portion 146 (see FIGS. 3 and 6). Unlike the outer inlet 144a, the outer outlet 147a is not disposed on the side of the outer protective cover 140 (the side 146a of the tip portion 146 in this embodiment). The outer outlet 147a (here, the vertical hole 147c) is a circular hole. The diameter of the outer outlet 147a is, for example, 0.5 mm to 2.5 mm. The diameter of the outer outlet 147a may be 1.5 mm or less. In this embodiment, the diameter of the vertical hole 147c is larger than the diameters of the horizontal hole 144b and the vertical hole 144c.

[0039] As described above, the outer protective cover 140 and the inner protective cover 130 form the inlet-side gas flow path 152 and the outlet-side gas flow path 156. The inlet-side gas flow path 152 includes the outer inlet 144a, the first gas chamber 122, and the element chamber inlet 125, and the measurement gas passes through the inlet-side gas flow path 152 in this order. The outlet-side gas flow path 156 includes the element chamber outlet 138a, the second gas chamber 126, and the outer outlet 147a, and the measurement gas passes through the outlet-side gas flow path 156 in this order. The first gas chamber 122 is formed as a space between the body portion 143 and the inner protective cover 130. More specifically, the first gas chamber 122 is a space surrounded by the stepped portion 133, the first cylindrical portion 134, the second cylindrical portion 136, the side portion 143a, and the stepped portion 143b. The second gas chamber 126 is formed as a space between the tip portion 146 and the inner protective cover 130. More specifically, the second gas chamber 126 is a space surrounded by the step portion 137a, the tip portion 138, and the tip portion 146. Note that, since the inner peripheral surface of the tip portion 146 abuts against the outer peripheral surface of the third cylindrical portion 137, the first gas chamber 122 and the second gas chamber 126 do not directly communicate with each other.

[0040] 3 and 7, the first gas chamber 122 has a first flow path 122a. The first flow path 122a is a space between the outer protective cover 140 and the second member 135 of the inner protective cover 130, and is a flow path for the measurement gas that flows upward from the outer inlet 144a. More specifically, the first flow path 122a is a space surrounded by the side portion 143a, the step portion 143b, and the second cylindrical portion 136, and is a space below the upper end of the second member 135 (here, the upper end of the second cylindrical portion 136). The first flow path 122a is a cylindrical gap between the inner circumferential surface of the outer protective cover 140 and the outer circumferential surface of the second cylindrical portion 136.

[0041] Next, the flow of the measurement gas inside the protective cover 120 when the gas sensor 100 detects the concentration of a specific gas will be described. The measurement gas flowing inside the pipe 10 first flows into the first gas chamber 122 through at least one of the multiple outer inlets 144a (here, the horizontal hole 144b and the vertical hole 144c). The measurement gas then moves upward inside the first flow path 122a and then flows into the sensor element chamber 124 through the element chamber inlet 125. More specifically, a portion of the measurement gas moving upward inside the first flow path 122a moves downward through the first inlet 127, flows out through the lower opening 127b, and flows into the sensor element chamber 124. A portion of the measurement gas passes through the second inlet 128 and flows into the sensor element chamber 124. At least a portion of the measurement gas that flows into the sensor element chamber 124 reaches the gas inlet 21 of the sensor element 110. The measurement gas flowing into the sensor element chamber 124 from the lower opening 127b passes upward through the opening 134c before reaching the gas inlet 21. When the measurement gas reaches the gas inlet 21 and flows into the sensor element 110, the sensor element 110 generates an electrical signal (voltage or current) corresponding to the concentration of a specific gas in the measurement gas, and the concentration of the specific gas is detected based on this electrical signal. The measurement gas in the sensor element chamber 124 flows into the second gas chamber 126 through at least one of the element chamber outlets 138a (here, the horizontal hole 138b). The measurement gas that reaches the sensor element 110 and reaches the inside of the first member 131 in the sensor element chamber 124 passes downward through the opening 134c and then flows into the second gas chamber 126 through the element chamber outlet 138a. The gas that reaches the second gas chamber 126 flows out through the outer outlet 147a. The output of the internal heater of the sensor element 110 is controlled by, for example, a controller (not shown) so as to maintain a predetermined temperature.

[0042] Here, the measurement gas may contain water, which may enter the protective cover 120 through the outer inlet 144a along with the measurement gas. If the water reaches the sensor element chamber 124 and adheres to the sensor element 110, cracks may occur in the sensor element 110 (particularly the element body 20). In the gas sensor 100 of this embodiment, as described above, the first member 131 has the bottom 134a disposed below the first cylindrical portion 134, and the opening area Sf of the opening 134c of the bottom 134a is smaller than the cross-sectional area S0 of the first cylindrical portion 134. The presence of such a bottom 134a in the first member 131 can prevent water from adhering to the sensor element 110 when water enters the sensor element chamber 124 through the first inlet 127. This improves the water resistance of the sensor element 110 in the gas sensor 100. This is because the part of the bottom 134a other than the opening 134c (here, the tapered part 134b) functions as a water adhesion prevention part that prevents water that enters the sensor element chamber 124 (inside the second member 135) from the first inlet 127 from adhering to the sensor element 110.

[0043] FIG. 8 is an explanatory diagram showing water W accumulated inside the inner protective cover 130. FIG. 8 shows the gas sensor 100 fixed inside the pipe 10 with its central axis tilted by 60° relative to the vertical. When the gas sensor 100 is disposed in this tilted state, water W that enters the inner protective cover 130 through the first inlet 127 tends to accumulate in the corner between the second cylindrical portion 136 and the stepped portion 136c, the corner between the third cylindrical portion 137 and the stepped portion 137a, and the corner between the side portion 138d and the bottom portion 138e. When the gas sensor 100 vibrates due to, for example, vehicle vibration, the accumulated water W may splash inside the inner protective cover 130 and adhere to the sensor element 110. However, as shown in FIG. 8 , in the gas sensor 100 of this embodiment, the bottom 134a is present between the inner circumferential surface of the second cylindrical portion 136 of the sensor element chamber 124 (particularly the inner circumferential surface of the corner portion) and the sensor element 110. This prevents splashed water W from adhering to the sensor element 110. This improves the water resistance of the sensor element 110 in the gas sensor 100. In contrast, if the first member 131 does not have the bottom 134a, as in the gas sensor 900 of the comparative example shown in FIG. 9 , water is likely to adhere to the sensor element 110. Note that if the sensor element chamber 124 is not tilted as shown in FIG. 8 , water that enters the inner protective cover 130 from the first inlet 127 is likely to collect at the bottom 138e. However, even in this case, the presence of the bottom 134a provides the effect of preventing splashed water from adhering to the sensor element 110.

[0044] The opening area Sf is 61.93 mm 2 In this way, the effect of improving the water resistance of the sensor element can be more reliably obtained. 2 It can be less than 40mm 2 It can be less than 30mm 2 It can be less than 28.27mm 2 It can be less than 25mm 2 The smaller the opening area Sf, the greater the effect of improving the water resistance of the sensor element.

[0045] The opening area Sf is 8.45 mm 2 If the opening area Sf is too small, the time it takes for the measurement gas to pass through the opening 134c and reach the sensor element 110 increases, which may result in a decrease in the responsiveness of the sensor element 110 in detecting the concentration of a specific gas. 2 By exceeding this limit, it is possible to suppress a decrease in the response time for detecting the concentration of a specific gas. 2 It can be more than 11.0mm 2 It can be more than 12.57mm 2 It can be more than 20mm 2 The larger the opening area Sf, the more likely it is that the decrease in responsiveness in detecting the concentration of a specific gas can be suppressed.

[0046] The vertical distance L (see FIG. 7) between the opening 134c and the gas inlet 21 may be, for example, 1 mm or more, or 7 mm or less.

[0047] Furthermore, in the gas sensor 100 of this embodiment, the element chamber inlet 125 has not only the first inlet 127 but also the second inlet 128, as described above. This allows the measurement gas to flow more easily into the sensor element chamber 124 than if the second inlet 128 were not present. This makes it possible to suppress a decrease in the responsiveness of the sensor element 110 in detecting the concentration of a specific gas. As described above, in the gas sensor 100 of this embodiment, the bottom portion of the bottom 134a is present between the first inlet 127 and the sensor element 110. While the bottom portion 134a improves the water resistance of the sensor element 110, there is a risk that the responsiveness of the sensor element 110 in detecting the concentration of a specific gas may decrease. In contrast, the presence of the second inlet 128 in addition to the first inlet 127 suppresses a decrease in responsiveness.

[0048] The opening area Ss of the second inlet 128 is 10.60 mm 2If the second inlet 128 is present, water may enter the sensor element chamber 124 not only from the first inlet 127 but also from the second inlet 128. 2 By keeping the opening area Ss below 10 mm, water is less likely to enter the sensor element chamber 124 through the second inlet 128, and therefore the presence of the second inlet 128 does not reduce the water resistance of the sensor element 110. When the second inlet 128 is made up of multiple holes as in this embodiment, the opening area Ss is the total value of the opening areas of the multiple holes. The opening area Ss is 10 mm 2 It can be less than 7.36mm 2 It can be less than 6.79mm 2 The smaller the opening area Ss, the greater the effect of improving the water resistance of the sensor element tends to be.

[0049] The opening area Ss is 1.18 mm 2 This makes it easier for the measurement gas to enter the sensor element chamber 124 through the second inlet 128, so the presence of the second inlet 128 more reliably suppresses a decrease in the response of the detection of the specific gas concentration. 2 It can be more than 2.65mm 2 It can be more than 3.12mm 2 The larger the opening area Ss, the more likely it is that the deterioration of the response of the detection of the specific gas concentration can be suppressed. The sum of the opening area Sf and the opening area Ss is 17.28 mm 2 It can be more than 24.77mm 2 It can be more than 26.24mm 2 It may be more than that.

[0050] According to the gas sensor 100 of this embodiment described above, the presence of the bottom portion 134a can prevent water from adhering to the sensor element 110 when water enters the sensor element chamber 124 from the first inlet 127. This can improve the water resistance of the sensor element 110 in the gas sensor 100. In addition, when the opening area Sf is 61.93 mm 2When the opening area Sf is less than 28.27 mm , the effect of improving the water resistance of the sensor element 110 can be more reliably obtained. 2 When the opening area Sf is 8.45 mm or less, the water resistance of the sensor element 110 is further improved. 2 By exceeding this limit, it is possible to suppress the decrease in response time for detecting the concentration of a specific gas. 2 As a result, it is possible to more reliably prevent a decrease in responsiveness in detecting the concentration of a specific gas.

[0051] Furthermore, since the element chamber inlet 125 has not only the first inlet 127 but also the second inlet 128, the measurement gas can easily flow into the sensor element chamber 124. This makes it possible to suppress a decrease in the responsiveness of the sensor element 110 in detecting the concentration of a specific gas. In addition, the opening area Ss of the second inlet 128 is 10.60 mm 2 By setting the opening area Ss to 7.36 mm or less, water is less likely to enter the sensor element chamber 124 from the second inlet 128, and therefore the water resistance of the sensor element 110 is less likely to decrease even if the second inlet 128 is present. 2 By setting the opening area Ss to 1.18 mm or less, it is possible to further suppress a decrease in the water resistance of the sensor element 110 due to the presence of the second inlet 128. 2 With the above, the effect of suppressing a decrease in the response of the detection of the concentration of a specific gas due to the presence of the second inlet 128 can be more reliably obtained. 2 As described above, the presence of the second inlet can more effectively suppress a decrease in responsiveness in detecting the concentration of a specific gas.

[0052] It goes without saying that the present invention is not limited to the above-described embodiment, and can be embodied in various forms as long as they fall within the technical scope of the present invention.

[0053] For example, in the above-described embodiment, the bottom portion 134a has a tapered portion 134b whose inner diameter decreases toward the bottom. However, this is not limited to this. It is sufficient that the bottom portion 134a has a shape in which the inner diameter decreases toward the bottom. For example, the bottom portion 134a may have a stepped portion so that the inner diameter decreases in a stepped manner toward the bottom. Alternatively, as in the gas sensor 200 of a modified example shown in FIG. 10, the bottom portion 234a does not have a shape in which the inner diameter decreases toward the bottom. The bottom portion 234a in FIG. 10 has a flat portion 234b perpendicular to the up-down direction and an opening 234c. The opening area Sf of the opening 234c is smaller than the cross-sectional area S0 of the first cylindrical portion 134. This gas sensor 200 also achieves the same effects as the above-described embodiment due to the same features. For example, the presence of the bottom portion 234a can improve the water resistance of the sensor element 110.

[0054] In the above-described embodiment, the inner protective cover 130 and / or the outer protective cover 140 may have a water passage suppression portion disposed above the outer inlet 144a of the first flow path 122a and shaped to narrow a portion of the first flow path 122a. For example, in a modified gas sensor 300 shown in FIG. 11 , the second cylindrical portion 136 of the second member 135 of the inner protective cover 130 has a water passage suppression portion 136b that protrudes radially outward. The water passage suppression portion 136b is located at the upper end of the second member 135, i.e., the upper end of the second cylindrical portion 136. The water passage suppression portion 136b has a tapered shape that expands in diameter from bottom to top. The water passage suppression portion 136b is disposed above the outer inlet 144a of the first flow path 122a and narrows a portion of the first flow path 122a. In this gas sensor 300, the water passage suppression portion 136b can suppress the upward movement of water that has entered the first flow path 122a from the outer inlet 144a. This makes it difficult for water to reach the element chamber inlet 125, and therefore the sensor element chamber 124. Therefore, the water resistance of the sensor element 110 can be improved not only by the bottom 134a of the first member 131 but also by the water passage suppression portion 136b.

[0055] In the above-described embodiment, the second inlet 128 is a plurality of holes, but it is not limited to this and may be a single hole. However, it is preferable that there are a plurality of second inlets 128, more preferably four or more, and even more preferably six or more.

[0056] In the above-described embodiment, the opening 134c is a single hole, but the opening 134c may be a plurality of holes. In this case, the opening area Sf is the total area of ​​the openings of the plurality of holes.

[0057] In the above-described embodiment, the element chamber inlet 125 has the first inlet 127 and the second inlet 128, but the second inlet 128 does not necessarily have to be present.

[0058] In the above-described embodiment, the second inlet 128 is located above the first inlet 127, but this is not limiting. For example, the second inlet 128 may be located below the upper opening 127a of the first cylindrical portion 134. In this case, the second inlet 128 opens midway through the flow path of the first inlet 127. In this case, part of the measurement gas that enters the first inlet 127 from the upper opening 127a enters the sensor element chamber 124 from the second inlet 128, and the remainder enters the sensor element chamber 124 from the lower opening 127b.

[0059] In the above-described embodiment, the outer inlet 144a has the horizontal hole 144b and the vertical hole 144c, but this is not limited thereto. The outer inlet 144a only needs to have at least the horizontal hole 144b. For example, as shown in Fig. 12, the outer inlet 144a may have a square hole 144d disposed at the corner of the boundary between the side portion 143a and the bottom portion (step portion 143b) of the body portion 143 in addition to or instead of the vertical hole 144c.

[0060] In the above-described embodiment, the inner protective cover 130 includes two members, the first member 131 and the second member 135, but the first member 131 and the second member 135 may also be an integrated member.

[0061] In the above-described embodiment, the gas inlet 21 is open to the front end surface of the sensor element 110 (the lower surface of the sensor element 110 in FIG. 3), but this is not limiting. For example, the gas inlet 21 may be open to a side surface of the sensor element 110 (any of the upper, lower, left, or right surfaces of the sensor element 110 in FIG. 4).

[0062] In the above-described embodiment, the sensor element 110 includes the porous protective layer 22, but the sensor element 110 may not include the porous protective layer 22.

[0063] 9, the front end (lower end) of the element body 20 of the sensor element 110 protrudes downward from the lower end of the first cylindrical portion 134. However, the front end of the element body 20 may be located above the lower end of the first cylindrical portion 134. In this case, the vertical distance between the front end of the element body 20 and the lower end of the first cylindrical portion 134 may be 5 mm or less, or may be greater than 5 mm. In other words, the front end of the element body 20 may be located above the lower end of the first cylindrical portion 134 by a distance greater than 5 mm. [Example]

[0064] Specific examples of fabricated gas sensors will be described below as examples. Experimental Examples 1 to 4 and 6 to 10 correspond to examples of the present invention, and Experimental Example 5 corresponds to a comparative example. Note that the present invention is not limited to the following examples.

[0065] [Experimental Examples 1-4] 3 to 7 were fabricated with different opening areas Sf to form Experimental Examples 1 to 4. In all of Experimental Examples 1 to 4, the cross-sectional area S0 of the first cylindrical portion 134 was 61.93 mm 2 The second inlet 128 is made up of six horizontal holes with a radius of 0.5 mm (therefore, the opening area Ss is 4.71 mm 2 The opening area Sf in Experimental Examples 1 to 4 was 8.45 mm 2 , 12.57mm 2 , 23.59mm 2 , 28.27mm 2 Other than that, Experimental Examples 1 to 4 had the same structure.

[0066] [Experimental Example 5] 9 was fabricated as Experimental Example 5. In Experimental Example 5, the cross-sectional area S0 and the opening area Ss were the same as in Experimental Examples 1 to 4. Since Experimental Example 5 does not have the bottom portion 134a, the opening at the lower end of the second cylindrical portion 136 was considered to correspond to the opening 134c, and the value of the opening area Sf was 61.93 mm 2 (same value as cross-sectional area S0).

[0067] [Experimental Examples 6-10] Experimental Examples 6 to 10 were prepared by fabricating the same gas sensor 100 as in Experimental Example 3, except that the radius of the second inlet 128 was changed to make the opening area Ss different from one another. The opening area Ss of Experimental Examples 6 to 10 was 1.18 mm 2 , 2.65mm 2 , 4.71mm 2 , 7.36mm 2 , 10.60mm 2 Other than that, Experimental Examples 6 to 10 had the same structure. As can be seen from the value of the opening area Ss, Experimental Example 8 is substantially the same gas sensor 100 as Experimental Example 3.

[0068] [Water resistance evaluation] The water resistance of the sensor element 110 of the gas sensors 100 of Experimental Examples 1 to 10 was evaluated. The water resistance evaluation was performed using a water exposure test apparatus described in Japanese Patent Application Laid-Open No. 2019-158615. This water exposure test apparatus includes a horizontal, linear pipe with a gas flow path therein, a blower installed upstream of the pipe, a pressure fluctuation generator installed downstream of the pipe, and a chamber located in a portion of the pipe between the blower and the pressure fluctuation generator, in which the gas sensor 100 is mounted. A vibrator that applies vibrations to the chamber is connected to the chamber. This water exposure test apparatus can disperse water toward the gas sensor 100 using gas simulating engine exhaust gas. In the water exposure test, the gas sensor 100 was first placed in the chamber of the water exposure test apparatus with its central axis perpendicular to the axis of the pipe and tilted 10° from the horizontal. Next, a predetermined amount of water was supplied into the pipe between the blower and the chamber. Next, a gas (atmospheric air) was supplied into the piping using a blower, the gas pressure was fluctuated using a pressure fluctuation generator, and vibrations were applied to the chamber using a vibrator. As a result, the moisture supplied into the piping was scattered toward the gas sensor 100 placed in the chamber by the gas with fluctuating pressure. In this state, the heater built into the sensor element 110 was driven, and the heater power was controlled so that the temperature of the sensor element 110 reached 850°C. If water adheres to the sensor element 110 at this temperature, cracks will occur in the sensor element 110, causing the electrical signal to indicate an abnormal value. Therefore, the presence or absence of cracks in the sensor element 110 was determined depending on whether the electrical signal indicated an abnormal value during the water exposure test. Five gas sensors 100 for each of Experimental Examples 1 to 10 were fabricated and subjected to the above-mentioned water exposure test. If none of the five gas sensors 100 had a crack in the sensor element 110, the gas sensors were judged to have very high water resistance ("A"); if one to three of the five gas sensors 100 had a crack in the sensor element 110, the gas sensors were judged to have high water resistance ("B"); and if four or all five gas sensors 100 had a crack in the sensor element 110, the gas sensors were judged to have low water resistance ("F").

[0069] [Responsiveness evaluation] The gas sensors 100 of Experimental Examples 1 to 10 were each attached to a pipe 10 as shown in FIGS. 1 and 2. A gas adjusted to an arbitrary oxygen concentration by mixing atmospheric air with oxygen was used as the measurement gas. This measurement gas was flowed through the pipe 10 at a flow rate of 7 m / s. The output (electrical signal) of the sensor element 110 was measured over time when the oxygen concentration of the measurement gas flowing through the pipe was varied. The output value of the sensor element immediately before the oxygen concentration was changed was defined as 0%, and the output value when the sensor element output changed and stabilized after the oxygen concentration change was defined as 100%. The response time (sec) for detecting the specific gas concentration was defined as the elapsed time from when the output value exceeded 10% to when it exceeded 90%. A shorter response time indicates a higher response for detecting the specific gas concentration. The response time was measured multiple times for each experiment, and the average of the measurements was defined as the response time for each experiment. If the response time was less than 0.5 seconds, the responsiveness was judged to be very high ("A"), if the response time was 0.5 seconds or more but less than 0.69 seconds, the responsiveness was judged to be high ("B"), and if the response time was 0.69 seconds or more, the responsiveness was judged to be low ("F").

[0070] The presence or absence of the bottom 134a and the opening area Sf [mm 2 ], opening area Ss[mm 2 The results of the water resistance assessment and the response evaluation are shown in Table 1.

[0071] [Table 1]

[0072] As shown in Table 1, experimental example 1, which did not have the bottom 134a and therefore had an opening area Sf that was not smaller than the cross-sectional area S0, was evaluated as "F" for water resistance, whereas experimental examples 1 to 4 and 6 to 10, which had the bottom 134a and had an opening area Sf smaller than the cross-sectional area S0, were all evaluated as "A" or "B" for water resistance. These results confirm that the presence of the bottom 134a and an opening area Sf smaller than the cross-sectional area S0 can improve the water resistance of the sensor element 110 in the gas sensor 100. Furthermore, experimental example 5, which had an opening area Sf of 61.93 mm 2Therefore, the opening area Sf is 61.93 mm 2 Furthermore, all of Experimental Examples 1 to 4, which have the same opening area Ss, were evaluated as "A" in terms of water resistance, and the largest opening area Sf among Experimental Examples 1 to 4 was 28.27 mm for Experimental Example 4. 2 Therefore, from the viewpoint of water resistance, the opening area Sf is 28.27 mm 2 Furthermore, among Experimental Examples 1 to 4, which have the same opening area Ss, Experimental Example 1 was evaluated as "F" in response, and Experimental Examples 2 to 4 were evaluated as "A" in response. Therefore, from the viewpoint of response, the opening area Sf is 8.45 mm 2 Excess is preferred, 12.57mm 2 The above is considered to be more preferable.

[0073] Furthermore, among Experimental Examples 6 to 10, which have the same opening area Sf, Experimental Example 10 was evaluated as "B" for water resistance, and Experimental Examples 6 to 9 were evaluated as "A" for water resistance. Therefore, from the viewpoint of water resistance, the opening area Ss is 10.60 mm 2 Preferably less than 7.36mm 2 The following is considered more preferable: Among Experimental Examples 6 to 10, Experimental Example 6 was evaluated as "B" in response, and Experimental Examples 7 to 10 were evaluated as "A" in response. From the viewpoint of response, the opening area Ss is 1.18 mm 2 More than 2.65mm is preferable. 2 The above is considered to be more preferable. [Explanation of symbols]

[0074] 10 piping, 12 fixing member, 20 element body, 21 gas inlet, 22 porous protective layer, 100, 200, 300, 900 gas sensor, 101 element sealing body, 102 housing, 103 bolt, 104 supporter, 105 powder compact, 110 sensor element, 120 protective cover, 122 first gas chamber, 122a first flow path, 124 sensor element chamber, 125 element chamber inlet, 126 second gas chamber, 127 first inlet, 127a upper opening, 127b lower opening, 128 second inlet, 130 inner protective cover, 131 first member, 132 large diameter portion, 133 step portion, 134 first cylindrical portion, 134a bottom portion, 134b tapered portion, 134c opening, 135 second member, 136 Second cylindrical portion, 136a protruding portion, 136b water passage suppression portion, 136c stepped portion, 137 third cylindrical portion, 137a stepped portion, 138 tip portion, 138a element chamber outlet, 138b horizontal hole, 138d side portion, 138e bottom portion, 140 outer protective cover, 143 body portion, 143a side portion, 143b stepped portion, 144a outer inlet, 144b horizontal hole, 144c vertical hole, 144d square hole, 146 tip portion, 146a side portion, 146b bottom portion, 146c tapered portion, 147a outer outlet, 147c vertical hole, 152 inlet side gas flow passage, 156 outlet side gas flow passage, 234a bottom portion, 234b flat portion, 234c opening.

Claims

1. a sensor element having a front end and a rear end opposite to the front end, the sensor element having a gas inlet for introducing a measurement gas, the sensor element detecting a specific gas concentration of the measurement gas flowing into the sensor element through the gas inlet; a cylindrical inner protective cover having a sensor element chamber therein in which the front end of the sensor element and the gas inlet are disposed, the sensor element chamber having an element chamber inlet which is an inlet to the sensor element chamber and an element chamber outlet which is an outlet from the sensor element chamber; a cylindrical outer protective cover having an outer inlet through which the measurement gas enters from the outside and an outer outlet through which the measurement gas exits to the outside, the outer protective cover being disposed outside the inner protective cover; Equipped with the outer protective cover and the inner protective cover form an inlet-side gas flow path from the outside to the sensor element chamber, which includes the outer inlet and the element chamber inlet, and an outlet-side gas flow path from the sensor element chamber to the outside, which includes the element chamber outlet and the outer outlet, the inner protective cover includes a cylindrical first member that surrounds the sensor element, and a cylindrical second member that surrounds the first member and has the element chamber outlet, the element chamber inlet has a first inlet configured as a gap between the first member and the second member, an opening of the first inlet on the sensor element chamber side is parallel to the axial direction of the first member and opens downward, which is a direction from the rear end toward the front end of the sensor element, the first member has a first cylindrical portion surrounding the sensor element, and a bottom portion disposed below the first cylindrical portion and the sensor element and having an opening, an opening area Sf of the opening of the bottom portion is smaller than a cross-sectional area S0 perpendicular to the axial direction of the space inside the first cylindrical portion, The bottom portion has a stepped portion so that the inner diameter thereof decreases in a stepped manner toward the downward direction, and / or the bottom portion has a flat plate portion perpendicular to the axial direction of the first member. Gas sensor.

2. 2. The gas sensor according to claim 1, the bottom has the opening at the downward end; Gas sensor.

3. 3. The gas sensor according to claim 1, The opening area Sf is 61.93 mm 2 is less than Gas sensor.

4. 3. The gas sensor according to claim 1, The opening area Sf is 28.27 mm 2 Below is the Gas sensor.

5. 3. The gas sensor according to claim 1, The opening area Sf is 8.45 mm 2 It is excessive, Gas sensor.

6. 3. The gas sensor according to claim 1, The opening area Sf is 12.57 mm 2 That's all. Gas sensor.

7. 3. The gas sensor according to claim 1, The element chamber inlet has a second inlet disposed in the first member. Gas sensor.

8. 8. The gas sensor according to claim 7, The second inlet is located in an upward direction relative to the first inlet, the direction being opposite to the downward direction. Gas sensor.

9. 8. The gas sensor according to claim 7, The opening area Ss of the second inlet is 10.60 mm 2 Below is the Gas sensor.

10. 8. The gas sensor according to claim 7, The opening area Ss of the second inlet is 7.36 mm 2 Below is the Gas sensor.

11. 8. The gas sensor according to claim 7, The opening area Ss of the second inlet is 1.18 mm 2 That's all. Gas sensor.

12. 8. The gas sensor according to claim 7, The opening area Ss of the second inlet is 2.65 mm 2 That's all. Gas sensor.

13. 3. The gas sensor according to claim 1, the inlet-side gas flow path has a first flow path that is a space between the outer protective cover and the inner protective cover and that extends from the outer inlet toward an upward direction that is opposite to the downward direction, The inner protective cover and / or the outer protective cover has a water passage suppression portion that is disposed in the first flow path above the outer inlet and has a shape that narrows a part of the first flow path. Gas sensor.

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